1. Field of the Invention
The present invention relates to a thin film transistor substrate and a display device having the thin film transistor substrate. More particularly, the present invention relates to a thin film transistor substrate having a relatively low resistance wiring structure and a display device having the thin film transistor substrate.
2. Description of the Related Art
Generally, a thin film transistor (“TFT”) substrate is used to control a pixel in a liquid crystal display (“LCD”) device or an organic light emitting display (“OLED”) device.
The TFT substrate includes a scan line (or gate line) for transferring a scan signal and a data line (or source line) for transferring an image signal. The TFT substrate further includes a TFT electrically connected to the scan line and the data line, a pixel electrode electrically connected to the TFT, a gate insulation layer that electrically insulates the gate line and a protection layer that electrically insulates the TFT and the data line.
The TFT includes a gate electrode, an activation layer, a source electrode, a data electrode, the gate insulation layer and the protection layer. The gate electrode extends from the scan line. The activation layer corresponds to a channel. The source and drain electrodes are formed through a metal layer forming the data line. The TFT corresponds to a switching device that applies the image signal to the pixel electrode, based on the scan signal provided from the scan line.
As a display device becomes larger and a resolution power becomes enhanced, the scan line and the data line become longer and narrower, so that an electrical resistivity and a parasitic capacitance increase, thereby inducing distortion of the scan and image signals, respectively.
As a result, aluminum (Al) used for a conventional display device is replaced by silver (“Ag”) having lower electrical resistivity than that of aluminum. However, silver has a relatively weak adhesiveness with a glass substrate or a silicon layer, so that a silver wiring may easily separate from the glass substrate or the silicon layer, thus inducing a malfunction. Furthermore, silver is easily damaged by an etching solution used for etching the gate insulation layer.
In order to solve the above-mentioned problems, a wiring having a three-layered structure, including a silver layer disposed between two indium (“In”) oxide layers, has been recently developed. However, oxygen from the indium oxide layers reacts with silicon in the activation layer of the TFT to form silicon oxide (“SiO2”). The formation of the silicon oxide increases a required on-current (“Ion”) for turning on the TFT and lowers a required off-current (“Ioff”) for turning off the TFT. Therefore, driving the TFT may become more difficult with the formation of the silicon oxide.